@SnakesAndArrows in answering your question 'Is it that the alleged signatories do not understand that some studies - maybe ones carried out by my (or indeed Ben Goldacre’s) cat - are just not studies? Or are they saying the grading of the studies is invalid? Or that poor studies should be included and given as much weight as the good ones anyway??'
There is one other reason for academics disregarding/attempting to discredit that comes to mind - seeing the pre-print* from Dr Hane Muang mentioned above (link below) and consider some of the other Gender Critical academics listed, the Cass report will have set aside as unworthy/unreliable/unusable many sources that these researchers have created or cited, and based their own research on. As there seems to be a tenancy of circular citation this affects (I want to say infects) a lot of academic research in this area.
For example there is a table in Muang's paper showing the sources he drew on to justify claims that there was benefit and no overall harm (relative to no treatment) with PB and HRT. https://link.springer.com/article/10.1007/s11673-023-10313-z/tables/1 This lists 12 sources. Only five of these are mentioned in the Cass review and only two of that five were used by the York team. This is what the Cass review says about the other three...
Chen, et al. 2023
Prospective cohort study of 315 trans adolescents receiving HRT
15.40 The authors of a paper reporting on psychosocial outcomes of 315 young people treated with masculinising/feminising hormones (Chen et al., 2023) stated that the most common adverse event was suicidal ideation (11
participants [3.5%]) and two participants [0.6%] died by suicide. Suicidality at baseline was one of the exclusion criteria for this study.
'De Vries et al. (2014) is the original study of the Dutch protocol sample, which has marked differences to the population being treated currently, and as discussed had much stricter criteria for treatment.'
Kuper, et al. 2020
Prospective cohort study of 148 trans adolescents receiving PB and HRT
'Kuper et al. (2020) is a study with a one year follow up that showed very modest change. It fell into the group rated by the University of York research team as too low quality to be included in their synthesis of evidence on masculinising/feminising hormones (Taylor et al: M/F hormones).'
Muang's table summarises his very different take on the value of these sources
Chen, et al. 2023
'Trans adolescents who received HRT reported improvements in appearance congruence, affect, and life satisfaction, and decreases in depression and anxiety. HRT likely decreased depression and anxiety symptoms via the psychological mechanism of improving appearance congruence'.
de Vries, et al. 2014
'Trans people who received PB and HRT in adolescence reported improvements in psychological health and social well-being, including decreased depression and anxiety. Trans people who received PB and HRT in adolescence had similar levels of well-being to peers of similar ages from the general population.'
Kuper, et al. 2020
'Trans adolescents who received PB and HRT reported improvements in depression, anxiety, and body dissatisfaction.'
Gender academics researching in this area will not easily be brought to agree their source material and therefore their own research may be sub standard.
*Pre-prints are not accepted for publication yet (my understanding) so although Dr Muang's paper has 2000 views its not out of the woods yet (not fully reviewed). https://www.springer.com/gp/open-access/preprint-sharing/16718886